Java 动态代理实现解析

Java动态代理只能针对接口进行动态代理。如果需要对类进行实现代理可以使用:CGLIB,ASM等相关的操作字节码实现（在这里先只介绍下SUN 基于接口动态代理的实现）。

代码如下：

import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;

public class ProxyTest {
	public static void main(String[] args) {
		/* 设置此系统属性,让JVM生成的Proxy类写入文件.保存路径为：com/sun/proxy(如果不存在请手工创建) */
		System.getProperties().put("sun.misc.ProxyGenerator.saveGeneratedFiles", "true");
		System.out.println(Proxy.getProxyClass(IUser.class.getClassLoader(), IUser.class));
		IUser userImpl = (IUser) new DynamicProxy().bind(new UserImpl());
		System.out.println(userImpl.sayHello(" kevin LUAN"));
	}

	public static class DynamicProxy implements InvocationHandler {
		public Object target;

		public Object bind(Object target) {
			this.target = target;
			return Proxy.newProxyInstance(target.getClass().getClassLoader(), target.getClass().getInterfaces(), this);
		}

		@Override
		public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
			return method.invoke(target, args);
		}
	}

	public static interface IUser {
		public String sayHello(String speakString);
	}

	public static class UserImpl implements IUser {

		@Override
		public String sayHello(String speakString) {
			return "welcome " + speakString;
		}

	}
}

执行结果输出：

class com.sun.proxy.$Proxy0

welcome  kevin LUAN

接下来我们去看看生成的$Proxy0.class文件。

反编译后内容如下：

package com.sun.proxy;

import ProxyTest.IUser;
import java.lang.reflect.InvocationHandler;
import java.lang.reflect.Method;
import java.lang.reflect.Proxy;
import java.lang.reflect.UndeclaredThrowableException;

public final class $Proxy0 extends Proxy
  implements ProxyTest.IUser
{
  private static Method m1;
  private static Method m3;
  private static Method m0;
  private static Method m2;

  public $Proxy0(InvocationHandler paramInvocationHandler)
    throws 
  {
    super(paramInvocationHandler);
  }

  public final boolean equals(Object paramObject)
    throws 
  {
    try
    {
      return ((Boolean)this.h.invoke(this, m1, new Object[] { paramObject })).booleanValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final String sayHello(String paramString)
    throws 
  {
    try
    {
      return (String)this.h.invoke(this, m3, new Object[] { paramString });
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final int hashCode()
    throws 
  {
    try
    {
      return ((Integer)this.h.invoke(this, m0, null)).intValue();
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  public final String toString()
    throws 
  {
    try
    {
      return (String)this.h.invoke(this, m2, null);
    }
    catch (Error|RuntimeException localError)
    {
      throw localError;
    }
    catch (Throwable localThrowable)
    {
      throw new UndeclaredThrowableException(localThrowable);
    }
  }

  static
  {
    try
    {
      m1 = Class.forName("java.lang.Object").getMethod("equals", new Class[] { Class.forName("java.lang.Object") });
      m3 = Class.forName("ProxyTest$IUser").getMethod("sayHello", new Class[] { Class.forName("java.lang.String") });
      m0 = Class.forName("java.lang.Object").getMethod("hashCode", new Class[0]);
      m2 = Class.forName("java.lang.Object").getMethod("toString", new Class[0]);
      return;
    }
    catch (NoSuchMethodException localNoSuchMethodException)
    {
      throw new NoSuchMethodError(localNoSuchMethodException.getMessage());
    }
    catch (ClassNotFoundException localClassNotFoundException)
    {
      throw new NoClassDefFoundError(localClassNotFoundException.getMessage());
    }
  }
}

所有生成的Proxy对象都默认继承了Proxy类，并实现了代理目标对象所实现的接口。

从代码可知，代理类做的事其实很简单，所有的方法处理都会交到：InvocationHandler来处理